Motorola BSR 2000, Configuration And Management Manual

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Release 1.0 Configuring BGP
526360-001-00 Rev. B MGBI 12-47
If two ASs are connected in more than one place, you can change this value so that a
router chooses the optimal link to reach a specific prefix in or behind that AS. Unlike
the Local Preference attribute, the MED attribute is exchanged between ASs. When
BGP sends an update to another AS, the MED attribute is reset to 0.
Use the bgp always-compare-med command to compare MED attributes from
different neighbors in different ASs.
Example
In Figure 12-17 , Routers Los Angeles, New York, and Boston send updates regarding
network 155.30.0 to AS 200. Router Chicago only compares the MED attributes of
routes coming from Routers New York and Boston, because, by default, BGP only
compares MED attributes of routes coming from external neighbors that are in the
same AS. Router Chicago ignores the MED attribute coming from Router Los
Angeles even though it is smaller.
Figure 12-17 Configuring the MED
The following commands configure Router Chicago:
MOT(config)#router bgp 200
AS 100
155.30.0.0
AS 200
192.56.0.0
AS 300
LA
bgp0022
NY
3.3.3.2
6.6.6.1
155.30.0.0
MED=25
155.30.0.0
MED=150
155.30.0.0
MED=100
3.3.3.1
Boston
Chicago
7.7.7.2
4.4.4.1
5.5.5.1
5.5.5.2
7.7.7.1
4.4.4.2
6.6.6.2